AngularJS apps are great. Always consider the business case before moving to Angular. An important part of that case is the time and effort to get there. This guide describes the built-in tools for efficiently migrating AngularJS projects over to the Angular platform, a piece at a time.

Some applications will be easier to upgrade than others, and there are many ways to make it easier for yourself. It is possible to prepare and align AngularJS applications with Angular even before beginning the upgrade process. These preparation steps are all about making the code more decoupled, more maintainable, and better aligned with modern development tools. That means in addition to making the upgrade easier, you will also improve the existing AngularJS applications.

One of the keys to a successful upgrade is to do it incrementally, by running the two frameworks side by side in the same application, and porting AngularJS components to Angular one by one. This makes it possible to upgrade even large and complex applications without disrupting other business, because the work can be done collaboratively and spread over a period of time. The upgrade module in Angular has been designed to make incremental upgrading seamless.

There are many ways to structure AngularJS applications. When you begin to upgrade these applications to Angular, some will turn out to be much more easy to work with than others. There are a few key techniques and patterns that you can apply to future proof apps even before you begin the migration.

The AngularJS Style Guide collects patterns and practices that have been proven to result in cleaner and more maintainable AngularJS applications. It contains a wealth of information about how to write and organize AngularJS code - and equally importantly - how not to write and organize AngularJS code.

Angular is a reimagined version of the best parts of AngularJS. In that sense, its goals are the same as the AngularJS Style Guide's: To preserve the good parts of AngularJS, and to avoid the bad parts. There's a lot more to Angular than just that of course, but this does mean that following the style guide helps make your AngularJS app more closely aligned with Angular.

The Rule of 1 states that there should be one component per file. This not only makes components easy to navigate and find, but will also allow us to migrate them between languages and frameworks one at a time. In this example application, each controller, component, service, and filter is in its own source file.

The Folders-by-Feature Structure and Modularity rules define similar principles on a higher level of abstraction: Different parts of the application should reside in different directories and NgModules.

When an application is laid out feature per feature in this way, it can also be migrated one feature at a time. For applications that don't already look like this, applying the rules in the AngularJS style guide is a highly recommended preparation step. And this is not just for the sake of the upgrade - it is just solid advice in general!

When you break application code down into one component per file, you often end up with a project structure with a large number of relatively small files. This is a much neater way to organize things than a small number of large files, but it doesn't work that well if you have to load all those files to the HTML page with <script> tags. Especially when you also have to maintain those tags in the correct order. That's why it's a good idea to start using a module loader.

Using a module loader such as SystemJS, Webpack, or Browserify allows us to use the built-in module systems of TypeScript or ES2015. You can use the import and export features that explicitly specify what code can and will be shared between different parts of the application. For ES5 applications you can use CommonJS style require and module.exports features. In both cases, the module loader will then take care of loading all the code the application needs in the correct order.

当要把应用程序投入生产环境时，模块加载器也会让你把所有这些文件打成完整的产品包变得容易一些。

When moving applications into production, module loaders also make it easier to package them all up into production bundles with batteries included.

If part of the Angular upgrade plan is to also take TypeScript into use, it makes sense to bring in the TypeScript compiler even before the upgrade itself begins. This means there's one less thing to learn and think about during the actual upgrade. It also means you can start using TypeScript features in your AngularJS code.

Since TypeScript is a superset of ECMAScript 2015, which in turn is a superset of ECMAScript 5, "switching" to TypeScript doesn't necessarily require anything more than installing the TypeScript compiler and renaming files from *.js to *.ts. But just doing that is not hugely useful or exciting, of course. Additional steps like the following can give us much more bang for the buck:

For applications that use a module loader, TypeScript imports and exports (which are really ECMAScript 2015 imports and exports) can be used to organize code into modules.

可以逐步把类型注解添加到现有函数和变量上，以固定它们的类型，并获得其优点：比如编译期错误检查、更好的支持自动完成，以及内联式文档等。

Type annotations can be gradually added to existing functions and variables to pin down their types and get benefits like build-time error checking, great autocompletion support and inline documentation.

那些 ES2015 中新增的特性，比如箭头函数、let、const、默认函数参数、解构赋值等也可以逐渐添加进来，让代码更有表现力。

JavaScript features new to ES2015, like arrow functions, lets and consts, default function parameters, and destructuring assignments can also be gradually added to make the code more expressive.

服务和控制器可以转成类。这样它们就能一步步接近 Angular 的服务和组件类了，也会让升级变得简单一点。

Services and controllers can be turned into classes. That way they'll be a step closer to becoming Angular service and component classes, which will make life easier after the upgrade.

You can also do this in AngularJS, using component directives. These are directives that define their own templates, controllers, and input/output bindings - the same things that Angular components define. Applications built with component directives are much easier to migrate to Angular than applications built with lower-level features like ng-controller, ng-include, and scope inheritance.

要与 Angular 兼容，AngularJS 的组件型指令应该配置下列属性：

To be Angular compatible, an AngularJS component directive should configure these attributes:

Controller lifecycle hook methods $onInit(), $onDestroy(), and $onChanges() are another convenient feature that AngularJS 1.5 introduces. They all have nearly exact equivalents in Angular, so organizing component lifecycle logic around them will ease the eventual Angular upgrade process.

The ngUpgrade library in Angular is a very useful tool for upgrading anything but the smallest of applications. With it you can mix and match AngularJS and Angular components in the same application and have them interoperate seamlessly. That means you don't have to do the upgrade work all at once, since there's a natural coexistence between the two frameworks during the transition period.

One of the primary tools provided by ngUpgrade is called the UpgradeModule. This is a module that contains utilities for bootstrapping and managing hybrid applications that support both Angular and AngularJS code.

When you use ngUpgrade, what you're really doing is running both AngularJS and Angular at the same time. All Angular code is running in the Angular framework, and AngularJS code in the AngularJS framework. Both of these are the actual, fully featured versions of the frameworks. There is no emulation going on, so you can expect to have all the features and natural behavior of both frameworks.

What happens on top of this is that components and services managed by one framework can interoperate with those from the other framework. This happens in three main areas: Dependency injection, the DOM, and change detection.

You can make AngularJS services available for injection to Angular code by upgrading them. The same singleton instance of each service is shared between the frameworks. In Angular these services will always be in the root injector and available to all components.

You can also make Angular services available for injection to AngularJS code by downgrading them. Only services from the Angular root injector can be downgraded. Again, the same singleton instances are shared between the frameworks. When you register a downgraded service, you must explicitly specify a string token that you want to use in AngularJS.

In the DOM of a hybrid ngUpgrade application are components and directives from both AngularJS and Angular. These components communicate with each other by using the input and output bindings of their respective frameworks, which ngUpgrade bridges together. They may also communicate through shared injected dependencies, as described above.

The key thing to understand about a hybrid application is that every element in the DOM is owned by exactly one of the two frameworks. The other framework ignores it. If an element is owned by AngularJS, Angular treats it as if it didn't exist, and vice versa.

So normally a hybrid application begins life as an AngularJS application, and it is AngularJS that processes the root template, e.g. the index.html. Angular then steps into the picture when an Angular component is used somewhere in an AngularJS template. That component's template will then be managed by Angular, and it may contain any number of Angular components and directives.

更进一步说，你可以按照需要，任意穿插使用这两个框架。 使用下面的两种方式之一，你可以在这两个框架之间自由穿梭：

Beyond that, you may interleave the two frameworks. You always cross the boundary between the two frameworks by one of two ways:

Whenever you use a component that belongs to the other framework, a switch between framework boundaries occurs. However, that switch only happens to the elements in the template of that component. Consider a situation where you use an Angular component from AngularJS like this:

The DOM element <a-component> will remain to be an AngularJS managed element, because it's defined in an AngularJS template. That also means you can apply additional AngularJS directives to it, but not Angular directives. It is only in the template of the <a-component> where Angular steps in. This same rule also applies when you use AngularJS component directives from Angular.

The scope.$apply() is how AngularJS detects changes and updates data bindings. After every event that occurs, scope.$apply() gets called. This is done either automatically by the framework, or manually by you.

In Angular things are different. While change detection still occurs after every event, no one needs to call scope.$apply() for that to happen. This is because all Angular code runs inside something called the Angular zone. Angular always knows when the code finishes, so it also knows when it should kick off change detection. The code itself doesn't have to call scope.$apply() or anything like it.

Everything that happens in the application runs inside the Angular zone. This is true whether the event originated in AngularJS or Angular code. The zone triggers Angular change detection after every event.

In practice, you do not need to call $apply(), regardless of whether it is in AngularJS on Angular. The UpgradeModule does it for us. You can still call $apply() so there is no need to remove such calls from existing code. Those calls just trigger additional AngularJS change detection checks in a hybrid application.

When you downgrade an Angular component and then use it from AngularJS, the component's inputs will be watched using AngularJS change detection. When those inputs change, the corresponding properties in the component are set. You can also hook into the changes by implementing the OnChanges interface in the component, just like you could if it hadn't been downgraded.

Correspondingly, when you upgrade an AngularJS component and use it from Angular, all the bindings defined for the component directive's scope (or bindToController) will be hooked into Angular change detection. They will be treated as regular Angular inputs. Their values will be written to the upgraded component's scope (or controller) when they change.

Their details are quite different in architecture and implementation. In AngularJS, you add Angular assets to the angular.module property. In Angular, you create one or more classes adorned with an NgModule decorator that describes Angular assets in metadata. The differences blossom from there.

In a hybrid application you run both versions of Angular at the same time. That means that you need at least one module each from both AngularJS and Angular. You will import UpgradeModule inside the NgModule, and then use it for bootstrapping the AngularJS module.

To bootstrap a hybrid application, you must bootstrap each of the Angular and AngularJS parts of the application. You must bootstrap the Angular bits first and then ask the UpgradeModule to bootstrap the AngularJS bits next.

在 AngularJS 应用中有一个 AngularJS 的根模块，它用于引导 AngularJS 应用。

In an AngularJS application you have a root AngularJS module, which will also be used to bootstrap the AngularJS application.

Pure AngularJS applications can be automatically bootstrapped by using an ng-app directive somewhere on the HTML page. But for hybrid applications, you manually bootstrap via the UpgradeModule. Therefore, it is a good preliminary step to switch AngularJS applications to use the manual JavaScript angular.bootstrapmethod even before switching them to hybrid mode.

To begin converting your AngularJS application to a hybrid, you need to load the Angular framework. You can see how this can be done with SystemJS by following the instructions in Setup, selectively copying code from the QuickStart github repository.

This bare minimum NgModule imports BrowserModule, the module every Angular browser-based app must have. It also imports UpgradeModule from @angular/upgrade/static, which exports providers that will be used for upgrading and downgrading services and components.

In the constructor of the AppModule, use dependency injection to get a hold of the UpgradeModule instance, and use it to bootstrap the AngularJS app in the AppModule.ngDoBootstrap method. The upgrade.bootstrap method takes the exact same arguments as angular.bootstrap:

Once you're running a hybrid app, you can start the gradual process of upgrading code. One of the more common patterns for doing that is to use an Angular component in an AngularJS context. This could be a completely new component or one that was previously AngularJS but has been rewritten for Angular.

假设你有一个简单的用来显示英雄信息的 Angular 组件：

Say you have a simple Angular component that shows information about a hero:

If you want to use this component from AngularJS, you need to downgrade it using the downgradeComponent() method. The result is an AngularJS directive, which you can then register in the AngularJS module:

Note that this AngularJS is an element directive (restrict: 'E') called heroDetail. An AngularJS element directive is matched based on its name. The selector metadata of the downgraded Angular component is ignored.

Most components are not quite this simple, of course. Many of them have inputs and outputs that connect them to the outside world. An Angular hero detail component with inputs and outputs might look like this:

Note that even though you are in an AngularJS template, you're using Angular attribute syntax to bind the inputs and outputs. This is a requirement for downgraded components. The expressions themselves are still regular AngularJS expressions.

There's one notable exception to the rule of using Angular attribute syntax for downgraded components. It has to do with input or output names that consist of multiple words. In Angular, you would bind these attributes using camelCase:

[myHero]="hero"

[myHero]="hero"

但是从 AngularJS 的模板中使用它们时，你得使用中线命名法：

But when using them from AngularJS templates, you must use kebab-case:

Since this is an AngularJS template, you can still use other AngularJS directives on the element, even though it has Angular binding attributes on it. For example, you can easily make multiple copies of the component using ng-repeat:

So, you can write an Angular component and then use it from AngularJS code. This is useful when you start to migrate from lower-level components and work your way up. But in some cases it is more convenient to do things in the opposite order: To start with higher-level components and work your way down. This too can be done using the upgrade/static. You can upgrade AngularJS component directives and then use them from Angular.

Not all kinds of AngularJS directives can be upgraded. The directive really has to be a component directive, with the characteristics described in the preparation guide above. The safest bet for ensuring compatibility is using the component API introduced in AngularJS 1.5.

可升级组件的简单例子是只有一个模板和一个控制器的指令：

A simple example of an upgradable component is one that just has a template and a controller:

You can upgrade this component to Angular using the UpgradeComponent class. By creating a new Angular directive that extends UpgradeComponent and doing a super call inside its constructor, you have a fully upgraded AngularJS component to be used inside Angular. All that is left is to add it to AppModule's declarations array.

Upgraded components are Angular directives, instead of components, because Angular is unaware that AngularJS will create elements under it. As far as Angular knows, the upgraded component is just a directive - a tag - and Angular doesn't have to concern itself with its children.

An upgraded component may also have inputs and outputs, as defined by the scope/controller bindings of the original AngularJS component directive. When you use the component from an Angular template, provide the inputs and outputs using Angular template syntax, observing the following rules:

As a two-way binding: <my-component [(myValue)]="anExpression">. Since most AngularJS two-way bindings actually only need a one-way binding in practice, <my-component [myValue]="anExpression"> is often enough.

举个例子，假设 AngularJS 中有一个表示“英雄详情”的组件型指令，它带有一个输入属性和一个输出属性：

For example, imagine a hero detail AngularJS component directive with one input and one output:

When you are using a downgraded Angular component from an AngularJS template, the need may arise to transclude some content into it. This is also possible. While there is no such thing as transclusion in Angular, there is a very similar concept called content projection. upgrade/static is able to make these two features interoperate.

Angular 的组件通过使用 <ng-content> 标签来支持内容投影。下面是这类组件的一个例子：

Angular components that support content projection make use of an <ng-content> tag within them. Here's an example of such a component:

When running a hybrid app, you may encounter situations where you need to inject some AngularJS dependencies into your Angular code. Maybe you have some business logic still in AngularJS services. Maybe you want access to AngularJS's built-in services like $location or $timeout.

In these situations, it is possible to upgrade an AngularJS provider to Angular. This makes it possible to then inject it somewhere in Angular code. For example, you might have a service called HeroesService in AngularJS:

Many developers prefer to declare the factory provider in a separate ajs-upgraded-providers.ts file so that they are all together, making it easier to reference them, create new ones and delete them once the upgrade is over.

同时，建议导出 heroesServiceFactory 函数，以便 AOT 编译器可以拿到它们。

It's also recommended to export the heroesServiceFactory function so that Ahead-of-Time compilation can pick it up.

Note: The 'heroes' string inside the factory refers to the AngularJS HeroesService. It is common in AngularJS apps to choose a service name for the token, for example "heroes", and append the "Service" suffix to create the class name.

In this example you upgraded a service class. You can use a TypeScript type annotation when you inject it. While it doesn't affect how the dependency is handled, it enables the benefits of static type checking. This is not required though, and any AngularJS service, factory, or provider can be upgraded.

In addition to upgrading AngularJS dependencies, you can also downgrade Angular dependencies, so that you can use them from AngularJS. This can be useful when you start migrating services to Angular or creating new services in Angular while retaining components written in AngularJS.

You can take advantage of Ahead-of-time (AOT) compilation on hybrid apps just like on any other Angular application. The setup for an hybrid app is mostly the same as described in the Ahead-of-time Compilation chapter save for differences in index.html and main-aot.ts

In this section, you'll learn to prepare and upgrade an application with ngUpgrade. The example app is Angular PhoneCat from the original AngularJS tutorial, which is where many of us began our Angular adventures. Now you'll see how to bring that application to the brave new world of Angular.

This is actually a pretty good starting point. The code uses the AngularJS 1.5 component API and the organization follows the AngularJS Style Guide, which is an important preparation step before a successful upgrade.

The core, phone-detail, and phone-list modules are each in their own subdirectory. Those subdirectories contain the JavaScript code as well as the HTML templates that go with each particular feature. This is in line with the Folders-by-Feature Structure and Modularity rules.

You should also configure the TypeScript compiler with a tsconfig.json in the project directory as described in the TypeScript Configuration guide. The tsconfig.json file tells the TypeScript compiler how to turn your TypeScript files into ES5 code bundled into CommonJS modules.

Next, convert your current JavaScript files into TypeScript. Since TypeScript is a super-set of ECMAScript 2015, which in turn is a super-set of ECMAScript 5, you can simply switch the file extensions from .js to .ts and everything will work just like it did before. As the TypeScript compiler runs, it emits the corresponding .js file for every .ts file and the compiled JavaScript is what actually gets executed. If you start the project HTTP server with npm start, you should see the fully functional application in your browser.

有了 TypeScript，你就可以从它的一些特性中获益了。此语言可以为 AngularJS 应用提供很多价值。

Now that you have TypeScript though, you can start benefiting from some of its features. There's a lot of value the language can provide to AngularJS applications.

For one thing, TypeScript is a superset of ES2015. Any app that has previously been written in ES5 - like the PhoneCat example has - can with TypeScript start incorporating all of the JavaScript features that are new to ES2015. These include things like lets and consts, arrow functions, default function parameters, and destructuring assignments.

Another thing you can do is start adding type safety to your code. This has actually partially already happened because of the AngularJS typings you installed. TypeScript are checking that you are calling AngularJS APIs correctly when you do things like register components to Angular modules.

But you can also start adding type annotations to get even more out of TypeScript's type system. For instance, you can annotate the checkmark filter so that it explicitly expects booleans as arguments. This makes it clearer what the filter is supposed to do.

You can apply the same trick to the application's route configuration file in app.config.ts, where you are using the location and route services. By annotating them accordingly TypeScript can verify you're calling their APIs with the correct kinds of arguments.

The AngularJS 1.x type definitions you installed are not officially maintained by the Angular team, but are quite comprehensive. It is possible to make an AngularJS 1.x application fully type-annotated with the help of these definitions.

If this is something you wanted to do, it would be a good idea to enable the noImplicitAny configuration option in tsconfig.json. This would cause the TypeScript compiler to display a warning when there's any code that does not yet have type annotations. You could use it as a guide to inform us about how close you are to having a fully annotated project.

Another TypeScript feature you can make use of is classes. In particular, you can turn component controllers into classes. That way they'll be a step closer to becoming Angular component classes, which will make life easier once you upgrade.

AngularJS expects controllers to be constructor functions. That's exactly what ES2015/TypeScript classes are under the hood, so that means you can just plug in a class as a component controller and AngularJS will happily use it.

新的“电话列表(phone list)”组件控制器类是这样的：

Here's what the new class for the phone list component controller looks like:

What was previously done in the controller function is now done in the class constructor function. The dependency injection annotations are attached to the class using a static property $inject. At runtime this becomes the PhoneListController.$inject property.

The class additionally declares three members: The array of phones, the name of the current sort key, and the search query. These are all things you have already been attaching to the controller but that weren't explicitly declared anywhere. The last one of these isn't actually used in the TypeScript code since it's only referred to in the template, but for the sake of clarity you should define all of the controller members.

在电话详情控制器中，你有两个成员：一个是用户正在查看的电话，另一个是正在显示的图像：

In the Phone detail controller, you'll have two members: One for the phone that the user is looking at and another for the URL of the currently displayed image:

If you had any AngularJS services in the project, those would also be a good candidate for converting to classes, since like controllers, they're also constructor functions. But you only have the Phone factory in this project, and that's a bit special since it's an ngResource factory. So you won't be doing anything to it in the preparation stage. You'll instead turn it directly into an Angular service.

Having completed the preparation work, get going with the Angular upgrade of PhoneCat. You'll do this incrementally with the help of ngUpgrade that comes with Angular. By the time you're done, you'll be able to remove AngularJS from the project completely, but the key is to do this piece by piece without breaking the application.

Soon you can load Angular dependencies into the application via index.html, but first you need to do some directory path adjustments. You'll need to load files from node_modules and the project root instead of from the /app directory as you've been doing to this point.

Now you're able to serve everything from the project root to the web browser. But you do not want to have to change all the image and data paths used in the application code to match the development setup. For that reason, you'll add a <base> tag to index.html, which will cause relative URLs to be resolved back to the /app directory:

Now create the root NgModule class called AppModule. There is already a file named app.module.ts that holds the AngularJS module. Rename it to app.module.ajs.ts and update the corresponding script name in the index.html as well. The file contents remain:

The application is currently bootstrapped using the AngularJS ng-app directive attached to the <html> element of the host page. This will no longer work in the hybrid app. Switch to the ngUpgrade bootstrap method instead.

Note that you are bootstrapping the AngularJS module from inside ngDoBootstrap. The arguments are the same as you would pass to angular.bootstrap if you were manually bootstrapping AngularJS: the root element of the application; and an array of the AngularJS 1.x modules that you want to load.

@types/angular is declared as a UMD module, and due to the way UMD typings work, once you have an ES6 import statement in a file all UMD typed modules must also be imported via import statements instead of being globally available.

AngularJS is currently loaded by a script tag in index.html, which means that the whole app has access to it as a global and uses the same instance of the angular variable. If you used import * as angular from 'angular' instead, you'd also have to load every file in the AngularJS app to use ES2015 modules in order to ensure AngularJS was being loaded correctly.

This is a considerable effort and it often isn't worth it, especially since you are in the process of moving your code to Angular. Instead, declare angular as angular.IAngularStatic to indicate it is a global variable and still have full typing support.

The first piece you'll port over to Angular is the Phone service, which resides in app/core/phone/phone.service.ts and makes it possible for components to load phone information from the server. Right now it's implemented with ngResource and you're using it for two things:

把所有电话的列表加载到电话列表组件中。

For loading the list of all phones into the phone list component.

把一台电话的详情加载到电话详情组件中。

For loading the details of a single phone into the phone detail component.

你可以用 Angular 的服务类来替换这个实现，而把控制器继续留在 AngularJS 的地盘上。

You can replace this implementation with an Angular service class, while keeping the controllers in AngularJS land.

The @Injectable decorator will attach some dependency injection metadata to the class, letting Angular know about its dependencies. As described by the Dependency Injection Guide, this is a marker decorator you need to use for classes that have no other Angular decorators but still need to have their dependencies injected.

In its constructor the class expects to get the Http service. It will be injected to it and it is stored as a private field. The service is then used in the two instance methods, one of which loads the list of all phones, and the other loads the details of a specified phone:

Now that you are loading phone.service.ts through an import that is resolved by SystemJS, you should remove the <script> tag for the service from index.html. This is something you'll do to all components as you upgrade them. Simultaneously with the AngularJS to Angular upgrade you're also migrating code from scripts to modules.

At this point, you can switch the two components to use the new service instead of the old one. While you $inject it as the downgraded phone factory, it's really an instance of the Phone class and you annotate its type accordingly:

Now there are two AngularJS components using an Angular service! The components don't need to be aware of this, though the fact that the service returns observables and not promises is a bit of a giveaway. In any case, what you've achieved is a migration of a service to Angular without having to yet migrate the components that use it.

Upgrade the AngularJS components to Angular components next. Do it one component at a time while still keeping the application in hybrid mode. As you make these conversions, you'll also define your first Angular pipes.

Look at the phone list component first. Right now it contains a TypeScript controller class and a component definition object. You can morph this into an Angular component by just renaming the controller class and turning the AngularJS component definition object into an Angular @Component decorator. You can then also remove the static $inject property from the class:

The selector attribute is a CSS selector that defines where on the page the component should go. In AngularJS you do matching based on component names, but in Angular you have these explicit selectors. This one will match elements with the name phone-list, just like the AngularJS version did.

The new PhoneListComponent uses the Angular ngModel directive, located in the FormsModule. Add the FormsModule to NgModule imports, declare the new PhoneListComponent and finally add it to entryComponents since you downgraded it:

The AngularJS injector has an AngularJS router dependency called $routeParams, which was injected into PhoneDetails when it was still an AngularJS controller. You intend to inject it into the new PhoneDetailsComponent.

Unfortunately, AngularJS dependencies are not automatically available to Angular components. You must upgrade this service via a factory provider to make $routeParams an Angular injectable. Do that in a new file called ajs-upgraded-providers.ts and import it in app.module.ts:

You're using the property binding syntax around ng-class. Though Angular does have a very similar ngClassas AngularJS does, its value is not magically evaluated as an expression. In Angular, you always specify in the template when an attribute's value is a property expression, as opposed to a literal string.

You've wrapped the whole template in an ngIf that causes it only to be rendered when there is a phone present. You need this because when the component first loads, you don't have phone yet and the expressions will refer to a non-existing value. Unlike in AngularJS, Angular expressions do not fail silently when you try to refer to properties on undefined objects. You need to be explicit about cases where this is expected.

There is no upgrade method to convert filters into pipes. You won't miss it. It's easy to turn the filter function into an equivalent Pipe class. The implementation is the same as before, repackaged in the transform method. Rename the file to checkmark.pipe.ts to conform with Angular conventions:

Now update the AppModule to import this AppRoutingModule and also the declare the root AppComponent as the bootstrap component. That tells Angular that it should bootstrap the app with the rootAppComponent and insert its view into the host web page.

And since you are routing to PhoneListComponent and PhoneDetailComponent directly rather than using a route template with a <phone-list> or <phone-detail> tag, you can do away with their Angular selectors as well.

You no longer have to hardcode the links to phone details in the phone list. You can generate data bindings for each phone's id to the routerLink directive and let that directive construct the appropriate URL to the PhoneDetailComponent:

The Angular router passes route parameters differently. Correct the PhoneDetail component constructor to expect an injected ActivatedRoute object. Extract the phoneId from the ActivatedRoute.snapshot.params and fetch the phone data as before:

It is time to take off the training wheels and let the application begin its new life as a pure, shiny Angular app. The remaining tasks all have to do with removing code - which of course is every programmer's favorite task!

应用仍然以混合式应用的方式启动，然而这再也没有必要了。

The application is still bootstrapped as a hybrid app. There's no need for that anymore.

Also remove any downgradeInjectable() or downgradeComponent() you find, together with the associated AngularJS factory or directive declarations. Since you no longer have downgraded components, you no longer list them in entryComponents.

The external typings for AngularJS may be uninstalled as well. The only ones you still need are for Jasmine and Angular polyfills. The @angular/upgrade package and its mapping in systemjs.config.js can also go.

Tests can not only be retained through an upgrade process, but they can also be used as a valuable safety measure when ensuring that the application does not break during the upgrade. E2E tests are especially useful for this purpose.

The PhoneCat project has both E2E Protractor tests and some Karma unit tests in it. Of these two, E2E tests can be dealt with much more easily: By definition, E2E tests access the application from the outside by interacting with the various UI elements the app puts on the screen. E2E tests aren't really that concerned with the internal structure of the application components. That also means that, although you modify the project quite a bit during the upgrade, the E2E test suite should keep passing with just minor modifications. You didn't change how the application behaves from the user's point of view.

在转成 TypeScript 期间，你不用做什么就能让 E2E 测试正常工作。 但是当你想改成按照混合式应用进行引导时，必须做一些修改。

During TypeScript conversion, there is nothing to do to keep E2E tests working. But when you change the bootstrap to that of a Hybrid app, you must make a few changes.

When you start to upgrade components and their templates to Angular, you'll make more changes because the E2E tests have matchers that are specific to AngularJS. For PhoneCat you need to make the following changes in order to make things work with Angular:

When the bootstrap method is switched from that of UpgradeModule to pure Angular, AngularJS ceases to exist on the page completely. At this point, you need to tell Protractor that it should not be looking for an AngularJS app anymore, but instead it should find Angular apps from the page.

替换之前在 protractor-conf.js 中加入 ng12Hybrid，象这样：

Replace the ng12Hybrid previously added with the following in protractor-conf.js:

Also, there are a couple of Protractor API calls in the PhoneCat test code that are using the AngularJS $location service under the hood. As that service is no longer present after the upgrade, replace those calls with ones that use WebDriver's generic URL APIs instead. The first of these is the redirection spec:

For instance, in the phone detail component spec, you can use ES2015 features like arrow functions and block-scoped variables and benefit from the type definitions of the AngularJS services you're consuming:

Once you start the upgrade process and bring in SystemJS, configuration changes are needed for Karma. You need to let SystemJS load all the new Angular code, which can be done with the following kind of shim file:

Once done, you can load SystemJS and other dependencies, and also switch the configuration for loading application files so that they are not included to the page by Karma. You'll let the shim and SystemJS load them.

The unit test files themselves also need to be switched to Angular when their production counterparts are switched. The specs for the checkmark pipe are probably the most straightforward, as the pipe has no dependencies:

Finally, revisit both of the component tests when you switch to the Angular router. For the details component, provide a mock of Angular ActivatedRoute object instead of using the AngularJS $routeParams.